Soon, Nadal gained the upper hand, shaking off a hard fall onto his back on one point by whipping a cross-court backhand victor on the next to break for a 3-2 lead.
"Rafa is a fighter and he has a fantastic game".
For all that Nadal plays tennis as if he had just disturbed a burglar making off with his 17 grand slam trophies, he prefers victory by stealth, sapping opponents of the will to chase.
Both players have settled into a nice rhythm in the opening set and it was Nadal who kept a high level in the entire set, serving at 75% and losing only eight points on serve, avoiding deuces or tie breaks to keep the pressure on Delpo.
Nadal ended the four hour and 48 minute thriller with a backhand volley victor past a lunging Del Potro who ended the contest lying flat on his stomach.
The two-time victor will meet Novak Djokovic in the last four on Friday.
"The last set had a little bit of everything, great points, great rallies, he was hitting insane with his forehands".
Juan Martin del Potro advanced to the Wimbledon quarterfinals for the first time since 2013 after beating Gilles Simon 7-6 (1), 7-6 (5), 5-7, 7-6 (5). "In some ways he deserves to win as well", said Nadal after the breath-taking quarter-final.
Del Potro threw everything he could at Nadal in a pulsating match and even conjured the shot of the tournament as he acrobatically dived to his right to hit a fizzing forehand volley that ended a spellbinding 23-shot rally. I tried to resist, maintaining focus.
While you were watching the World Cup semi-final last night, and before that, while you were desperately trying to get out of work to go home and watch the World Cup semi-final, there was a day for ages playing out at Wimbledon, featuring, of course, Roger Federer and Rafa Nadal. The dogfight Nadal feared and Del Potro knew was his only route to the semi-finals had begun in earnest.
Del Potro too noted the change in conditions but appeared to relish the chance to slide around a bit more on the grass.
Nadal caught Del Potro napping in the fifth game, the big man slipping on the worn baseline dust as he was broken to love.
"I play Los Cabos in Mexico - the beach", he smiled.